> Yes, I am totally aware of the above, but, as there is absolutely no
> reason for the dng mails sent to me being bounced and that others have
> had this happen to them, I feel the problem could be at the dng end.

Maybe it is emergent (heh!) problem requiring a particular combination
of sending and receiving software ?

I see that smtp.samba.org seems to run exim - are the others
experiencing bounces and disabled subscriptions also running exim ?

Also: This isn't strictly a problem, but the highest priority
mail handler for samba.org doesn't seem to be running a mail server
at the moment:

samba.org.              7200    IN      MX      5 ns1.samba.org.
samba.org.              7200    IN      MX      9 ns1.samba.org.
samba.org.              7200    IN      MX      7 smtp.samba.org.

;; Query time: 441 msec
;; SERVER: 196.22.160.5#53(196.22.160.5)
;; WHEN: Fri Jan 4 21:26:52 2019
;; MSG SIZE rcvd: 84

~$ telnet ns1.samba.org 25
Trying 144.76.82.137...
Connection failed: Connection refused
Trying 2a01:4f8:192:486::b0...
telnet: Unable to connect to remote host: Network is unreachable

regards

marc